Operating on display


Secret Communications 3




Status: 25 October 2019



2 (25 October 2019)

We have reached the point where the German wartime speech scrambler: type GK IIIb system has been put on display as well as functioning operationally.

What should be looked after next, is, whether it is possible to increase the loudspeaker strength.


Therefore I would like to test whether it is possible to used a computer loudspeaker set. For it

I already obtained an 3.5 female plug and on the other end having two cinch male connectors.

because these thing are of an asymmetric nature in between I would like to adapt a 1 : 1 transformer and connecting it onto the 'Telefon' marked connections.  




Viewing our oldest GK IIIb scrambles in conjunction with the T 65 type telephone



Taking a closer view



Viewing at the second GK IIIb scrambler device, combined with a NA 6 power-supply unit; and in front in the Al box I have integrated the 2.1 V filament stabiliser circuitry

The cables on the left-hand side are connecting the various supply voltages feeding it onto both GK IIIb apparatus. 



The unit in the rear of the telephone apparatus constitutes a "cable equivalent"



Viewing it more in detail

It represents in total: 5 x 1km regular PTT ground cable equivalent; having a core diameter of 0.8 mm

Each red jumper connecting the equivalence of 1 km.

When removing two jumpers (symmetry!) in the line, the remaining cable equivalence is than the number of jumpers left x 1 km.


It proves that the system does not have any problems with such ground cable parameter.


Today, I returned in the afternoon to the Klooster again, and wired two cinch female connections in parallel and fed the mono output onto a 1 : 1 transformer which was connected onto the 'Telefon 'terminals.




I did function well instantly, and proves to be a real improvement

Now also the audibility has increased very much.

The the two Logitec speakers standing in the corner where formerly the wartime Lautsprechgerät stood.



The only disappointment was - the hum coming out of the loudspeakers

To solve this disadvantage was quite simple, connecting the metal of the system within the Logitec loudspeakers (simply connecting the outside of the cinch connectors with the ground of the NA 6 power supply; that is the grey coloured cable)






On  25 October 2019


Like we arranged during Secret Communications 2, we have created a spot where visitors can view or read book passages

The upper row is not to be touched, without strict permission; whereas the low row can be accessed freely, albeit, with care.



During Secret Communications 2 we also noticed that an old fashioned bureau-lamp is additionally attractive



The GK IIIb scrambler system has got new loudspeakers; but because I discovered that not all German Field telephones were brought into the depot; hence, why not trying one out in combination with the new loudspeakers?

But this was adapted after the next two YouTube films had been uploaded.

However, it operated better than had been encountered in conjunction with the German Lautsprechgerät; its descrambling result is reasonable, but I am not convinced in case of operating one on either sides.





YouTube Films:


Film 00043:    We have brought to function our GK IIIb scrambler modules again, now in the new Secret Communications 3 setup. But operating a T65 type telephone set again, and supplying it by means of a genuine wartime NA 6 unit. Hans is speaking, and his voice being made audible by means of a pair of Logitec loudspeakers. Useless devices;  due to it inferior music reproduction; but fitting well into our current display. A downside encountered, is, that when both scramblers being switched off - that an audible humm appears (50 or 100 Hz). I suppose the source being the simple line-current mains adapter. 



Film 00044:    Explained is our current power supply system. Relying upon a NA 6 unit. My aim being: changing nothing inside, so that it instantly can be operated in conjunction with a KWE-a or LWE-a receiver again. What is made use of, is, the voltage rise due to the less numbers of filaments than in case of a KWE-a:  6 valves maximally (2 x GK IIIb) versus 11 valves in case of operating a KWE-a. The filament supply generated, instead of, say, 2.1 V now 5-6 V. Just employed as to let a LM xx doing its proper voltage regulation (2.1 V).






To be continued in due course




By Arthur O. Bauer